1. Field of the Invention
The present invention relates to an electric fuel pump that pumps fuel.
2. Description of Related Art
Conventionally, a fuel pump that has a pump portion and a motor portion, which are placed in a case member, is known (see JPH07-091343A corresponding to U.S. Pat. No. 5,520,547, and JP2002-544425T corresponding to U.S. Pat. No. 6,478,613). FIG. 19 shows an entire construction of the fuel pump disclosed in JPH07-091343A corresponding to U.S. Pat. No. 5,520,547. As shown in FIG. 19, a discharge-side cover 1010 and case members 1020, 1030 define fuel passages 1013, 1042 therein. A fuel discharge port 1011 is formed in the discharge-side cover 1010. A fuel suction port 1031 is formed in the case member 1030. A holder 1040 is placed in the discharge-side cover 1010. The holder 1040 holds a positive brush and a negative brush that are placed inside the discharge-side cover 1010. The positive and negative brushes are in contact with a commutator of a motor portion 1050 to supply electric power from a positive terminal and a negative terminal 1012 to the motor portion 1050.
The motor portion 1050 includes an armature 1051. A pump portion 1060 includes an impeller 1061. The pump portion 1060 is driven by the motor portion 1050 to suck fuel from the fuel suction port 1031 and to pump the fuel to the fuel discharge port 1011.
FIG. 20 is an exploded cross-sectional view showing the discharge-side cover 1010 and the holder 1040, which are shown in FIG. 19. As shown in FIG. 20, the positive and negative terminals 1012 are fixed to the holder 1040. The electric power for driving the motor portion 1050 is supplied from an external electric power source to the positive and negative terminals 1012.
Arrows L1-L4 in FIG. 19 indicate fuel flow. When the pump portion 1060 drives, fuel is sucked into the fuel suction port 1031 (see the arrow L1). Then, the fuel flows through the fuel passage 1042 in the case member 1020 (see the arrow L2) and through the fuel passage 1013 in the discharge-side cover 1010 (see the arrow L3). Finally, the fuel is discharged out of the fuel discharge port 1011 (see the arrow L4).
The fuel pump disclosed in JPH07-091343A corresponding to U.S. Pat. No. 5,520,547 is a pump for gasoline fuel. However, in recent years, demand for alternative fuels that substitute for gasoline is increasing. The alternative fuels are concentrated alcohol fuel, bioethanol, 100% ethanol fuel, etc. These alternative fuels contain electrically conductive ingredients. Therefore, if a conventional pump for gasoline fuel is used as a fuel pump for pumping alternative fuels as it is, the following problem occurs.
In the fuel pump disclosed in JPH07-091343A corresponding to U.S. Pat. No. 5,520,547, the positive and negative terminals 1012 are fixed to a top surface of the holder 1040. The positive and negative terminals 1012 are exposed to a space in the fuel passage 1013. That is, whole bodies of the positive and negative terminals 1012 are exposed to the fuel (see the arrow L3 in FIG. 19). If the fuel contains the electrically conductive ingredients as mentioned above, electric current (hereafter referred to as leakage current) passes between the positive and negative terminals 1012. Thereby, the positive and negative terminals 1012 are subject to electrochemical corrosion (hereafter referred to just as electric corrosion) in areas exposed to the fuel. This causes poor electrical continuity at the positive and negative terminals 1012 and/or breakage of the positive and negative terminals 1012.